NWS Forecast Discussion
336
FXUS61 KCTP 031959
AFDCTP
Area Forecast Discussion
National Weather Service State College PA
259 PM EST Tue Dec 3 2024
.SYNOPSIS...
* Cold and breezy conditions continue this week with
temperatures below the historical average for early December
* Lake effect snow in Warren and McKean Counties shifts to the
north tonight then ramps back up late Wednesday night-Friday
* Widespread snow showers and a few squalls are likely late
Wednesday night into Thursday along with 30-50 mph wind gusts
&&
.NEAR TERM /UNTIL 7 PM THIS EVENING/...
Sfc trough axis tracking southward from the PA/NY border will
disrupt the heavier snow showers in the lake effect warning
area - but also help to deliver a broader area of mainly light
snow showers to the northern tier of CPA into midday. Hires
models suggest some mesoscale lake effect banding reestablishes
itself this afternoon extending southeast from Lake Erie [with
possible Huron connection] somewhere across the I80 corridor.
This may result in later adjustments to POPs, but for now we
added lower chances for snow showers/flurries through the
evening commute.
1540UTC GOES visible shows mostly sunny skies across the
majority of south central PA (outside of the Laurels) to the
south of the sfc trough axis. Arrival of slightly cooler air
aloft could lead to an uptick in stratocu into the afternoon and
latest trends would be generally supportive of increased cloud
cover particularly to the northwest of I81.
Daytime highs will be 5 to 10 degrees below the historical
average for early December ranging from the upper 20s in the
Allegheny Mtns to around 40F in the mid to lower Susquehanna
Valley.
For the Wed night-Thu sharp frontal system, we are considering
expanding the watch to include the Laurel Highlands later this
afternoon.
&&
.SHORT TERM /7 PM THIS EVENING THROUGH FRIDAY/...
As the llvl wind finally pushes the LES to the N, the influence
of a major sfc low deepening over the Canadian Plains will
already be beginning. Clouds aloft will be brought in from the
west in the warm-ish advection in advance of the fronts
associated with the storm. Not much of a moisture inflow as the
low passes north of the Great Lakes, headed to srn Quebec by
Thursday aftn, deepening to 990mb as it does so. The tight
pressure gradient between the suppressed high and the vigorous
low will generate a strong/gusty wind, peaking Wed evening/night
(starting before CFROPA) and lasting into/through much of Thursday
(in the strong CAA). 60+KT winds get down to just 3-4kft Wed
evening at JST and 50+KT wind gets that low at BFD and much of
the rest of the area. But, there will be a 70-90deg veer to the
wind from the sfc to that level. After the front passes, Even
the lower elevation of the SE could get gusts well into the 40s
on Thursday when the vertical alignment gets better there. The
push of arctic air is a classic setup for widespread SHSN/SNSQ,
but timing of frontal passage is at the diurnal minimum, likely
before sunrise Thurs. The wind will probably require an advy ,
but the confidence is not quite there to hoist it on this shift.
The SHSN will amount to little before sunset Wed, but an inch or
less is a good bet for the Alleghenies by then. As the stronger
SHSN and front move through, a very accum could happen all the
way to Lancaster Co. But, the temps will actually be marginal
for any snow to stick. Have mentioned more a rain-snow mix for
them for later Wed night. After that, it`s all cold, but drying
out in the (Thurs) morning.
It`s the lake effect that will cause the most trouble in the Wed
PM-Thurs PM time frame. Expect another good Huron connection,
with a slightly north of west fetch. The possibility of 6+"
over the 36 hrs is high enough to post a watch for that time
frame. Elk county may be the beneficiary of the more-NWrly and
fast flow. We`ve added them to the watch along with Warren and
McKean. The Laurels may get 1-3 out of the first pass of snow
Wed/night, and another 1-3 on Thurs/night. This will probably be
enough for an advy, but there could be much of the day Thurs
where they will only have flurries. A very complicated
situation. The rest of the nrn mtns is on target to have 1-3",
and AOO-UNV in the 1-2" range, mostly Wed PM. Some point amounts
over 3" are possible, but the wind will be so strong that the
flakes may get fractured and blown around so much that it may
not be easy to get it to build up.
The SLRs waggle around thru the event, but will probably be near
20:1 during the heaviest lake effect time. So, even with gusts
into the 30s (N) and 40s (S) at times, the worry for power
outages due to snow on the power lines is low but more than
zero.
Temps may waggle up a little Wed night before the FROPA,
especially in the S. They will then fall, and stay steady or may
even continue to fall slightly through the day almost
everywhere. The clouds and well-mixed llvls Thursday night won`t
allow much of a temp fall. But, wind chills will be in the
single digits NW and teens SE. Spots in the Laurels may touch 0F
wind chills.
A reinforcing shot of cold air will move in on Friday, with wind
chills in the single digits for western and northern zones
Friday morning, along with another bout of lake effect and
upslope snow.
&&
.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
Northwest flow in the cloud bearing layer will maintain a chance
for a heavier lake effect snow band in the Northwest zones
Friday night. By Saturday morning, a subsidence inversion will
descend towards the sfc and decrease the available instability
for the LES.
Ridging will begin building in Sunday, and height rises
combined with southerly flow will bring an end to any lake
effect snow by early Sunday, followed by moderating
temperatures for the beginning of next week.
A warm front will cross over Pennsylvania Sunday night into
Monday associated with a subtle shortwave. This will bring
mostly rain Sunday night into Tuesday, but there could be a
period of snow or freezing rain in coldest spots prior to
sunrise Monday. Highs in the 40s and 50s are progged for
Tuesday, which would feel much warmer than recent days.
&&
.AVIATION /20Z TUESDAY THROUGH SUNDAY/...
A shortwave trough moving through central PA this afternoon will
bring scattered snow showers mainly across the northern
airfields (BFD, IPT, and perhaps UNV). Most of the snow showers
are on the light side, but a few heavier bursts could bring the
vsby briefly to 1/2 SM. BFD and JST will see bkn cigs on the
cusp between high end VFR and low end MVFR. VFR conds are
expected elsewhere today and tonight.
Light snow flurries are possible on Wed ahead of an approaching
cold front. The strong cold front will cross the area Wed night,
with widespread snow showers, some heavy, Wed night into Thu.
Wind gusts are expected in the 30-45kt range from 270-320 deg
late Wed night into Thu.
Outlook...
Fri-Sat...IFR/MVFR most likely at KBFD/KJST with return of lake
effect and upslope snow showers. MVFR to low VFR expected
elsewhere. Decreasing wind.
Sun...Mostly VFR.
&&
.CTP WATCHES/WARNINGS/ADVISORIES...
Lake Effect Snow Warning until 7 PM EST this evening for
PAZ004-005.
Winter Storm Watch from Wednesday afternoon through late
Thursday night for PAZ004-005-010.
&&
$$
SYNOPSIS...Steinbugl
NEAR TERM...Steinbugl
SHORT TERM...Dangelo
LONG TERM...Colbert
AVIATION...Gartner/Colbert
NWS CTP Office Area Forecast Discussion
